NFS prevent double free in async nfs4_exchange_id

Since rpc_task is async, the release function should be called which
will free the impl_id, scope, and owner.

Trond pointed at 2 more problems:
-- use of client pointer after free in the nfs4_exchangeid_release() function
-- cl_count mismatch if rpc_run_task() isn't run

Fixes: 8d89bd70bc9 ("NFS setup async exchange_id")
Signed-off-by: Olga Kornievskaia <[e-mail]>
Cc: [e-mail] # 4.9
Signed-off-by: Anna Schumaker <[e-mail]>

fs/nfs/nfs4proc.c

···
 	struct nfs41_exchange_id_data *cdata =
 					(struct nfs41_exchange_id_data *)data;
 
-	nfs_put_client(cdata->args.client);
 	if (cdata->xprt) {
 		xprt_put(cdata->xprt);
 		rpc_clnt_xprt_switch_put(cdata->args.client->cl_rpcclient);
 	}
+	nfs_put_client(cdata->args.client);
 	kfree(cdata->res.impl_id);
 	kfree(cdata->res.server_scope);
 	kfree(cdata->res.server_owner);
···
 	task_setup_data.callback_data = calldata;
 
 	task = rpc_run_task(&task_setup_data);
-	if (IS_ERR(task)) {
-	status = PTR_ERR(task);
-		goto out_impl_id;
-	}
+	if (IS_ERR(task))
+		return PTR_ERR(task);
 
 	if (!xprt) {
 		status = rpc_wait_for_completion_task(task);
···
 	kfree(calldata->res.server_owner);
 out_calldata:
 	kfree(calldata);
+	nfs_put_client(clp);
 	goto out;
 }